HistoryThe following is taken from New York in the War of the Rebellion, 4th ed.
Frederick Phisterer. Albany: J. B. Lyon Company, 1912.

Under special orders of the War Department, dated May 8, 1865, this organization
was formed by the consolidation of the 3d
Cavalry and the 1st Mounted
Rifles;
the consolidation took place July 21, 1865, and September 6, 1865, and the
new regiment was designated as above. The companies were formed A, C, D, E,
G, K, and M, from the 1st Mounted Rifles and B, F, H, I, and L from the 3d
Cavalry, and Col. Edwin V. Sumner, of the 1st Mounted Rifles, was placed in
command of the regiment, which was honorably discharged and mustered out, under
his command, November 29, 1865, at City Point, Va., having lost by death, of
disease and other causes, ten enlisted men.